Hi,
You are correct. In his case, the PO is allowed to save and the stock is increased after GR. If its with item category L, system will always check for components and the PO is not allowed to save without components. If the components is there in PO, the same will be consumed during GR for the subcontract PO. So I guess he missed to maintain the item category and system considered it as normal purchasing or the component quantity was manually removed during MIGO.
Any way, lets wait for the reply from the OP.
Regards,
AKPT